Method of simultaneously electroplating and machining a metal surface

ABSTRACT

A conductive workpiece is simultaneously machined and electroplated by using a rotatable maching tool against the surface of the workpiece being electroplated and by delivering the electroplating solution thereto under high current density. The electroplating solution comprises an aqueous solution containing one of bronze, cobalt and chromium.

United States Patent [191 Biora et al.

[ 1 Oct. 30, 1973 [75] Inventors: Julio L. Biora, Detroit; Charles V.

Wilkie, Troy, both of Mich.

[73] Assignee: The Richardson Chemical Company,.

Des Plaines, Ill.

[22] Filed: July 21, 1971 [21] Appl. No.: 164,943

[52] U.S. Cl 204/35 R, 204/44, 204/48,

204/51, 204/DIG. 10 [51] Int. Cl C23b 5/48 [58] Field of Search 204/26, 35 R, 36, 204/44, 48, 51, DIG. 10

[56] References Cited UNITED STATES PATENTS 3,022,232 2/1962 Bailey et al. 204/36 3,440,151 4/1969 Duva et al. 204/44 2,640,022 5/1953 Stareck 204/51 3,616,289 10/1971 Ellis et a] 204/26 3,619,384 11/1971 Eisner 204/36 3,183,176 5/1965 Schwartz, Jr. 204/DIG. 10

v OTHER PUBLICATIONS Morral, F. R. Electroplating of Co and Co Alloys-A Review," Plating, June, 1967, pp. 693 and 695-696.

Endicott, D. W. et al., Electrodeposition of Ni-Co Alloy: Operating Variables and Physical Properties of the Deposits, Plating, 1/66 (Vol. 53, No. 1) pp. .43 & 46-47.

W. A. Wesley et a]. Electrodeposition of Nickel at High Current Density, Proceedings of the American Electroplaters Society, 1949, pp. 79-91, TS670A32.

Primary Examiner-John l-l. Mack Assistant Examiner-W. 1. Solomon Attorney-Cushman et a].

[5 7 ABSTRACT A conductive workpiece is simultaneously machined and electroplated by using a rotatable maching tool against the surface of the workpiece being electroplated and by delivering the electroplating solution thereto under high current density. The electroplating solution comprises an aqueous solution containing one of bronze, cobalt and chromium.

2 Claims, N0 Drawings METHOD OF SIMULTANEOUSLY ELECTROPLATING AND MACHINING A SURFACE This invention relates to a process for simultaneously electro'depositing a metal on a base member while at the same time machining the surface on which said metal is electrodeposited to desired specifications.

Heretofore metallic workpieces which were required to be plated and machined generally were initially METAL treated to deposit the desired metal thereon and thereafter, in a separate-and distinct operation, the thus plated metallic workpieces were machined to the desired specifications. Such separate operations were time consuming in that conventional plating periods often extended up to about 2 hours or more and additional time was consumed in transferring the workpieces from the plating site to the machining site. Further in conventional plating processes the maximum current densities generally utilized do not exceed amp/dm and the speed of deposition rarely exceeds 2 microns per minute. Furthermore, in these conventional plating operations soluble anodes are used to keep the chemical composition within accepted limits and air and cathode agitation are provided.

The present invention represents an improvement over such conventional operations and is especially suitable for sizing and electroplating an internal diameter of a metallic workpiece and thus finds wide application in salvage operations as well as in the formation of bushing or bearing deposits In one of its principle aspects, the invention thus resides in a method of simultaneously electroplating and honing the internal diameter a conductive workpiece utilizing apparatus comprising a rotatable honing tool which is controlled so that it forces its honing faces against the inside face of the hole in the workpiece to be machined.

With the use of such apparatus, the speed of deposition must be increased several-times to make it economically sound. These high deposition speeds are possible because of the strong agitation provided by the apparatus and the very short distance between anode and cathode which thus permits the use of ten times the current densities used in normal plating processes.

The workpiece is held essentially stationary in a workpiece holder associated with the apparatusand a plating solution is delivered from a reservoir across the surface to be plated while the honing tool is being rotated. Electroplating current is applied at very high current densities using the honing tool as the anode and the workpiece as the cathode. As the electrodeposit begins to build in thickness, the honing faces of the tool are retracted automatically and at a predetermined rate 3 so that the electroplate builds up uniformly at a high rate, and machined or honed while it increases. The operation can be automatically terminated when the required tolerances or specifications are reached.

The successful implementation of such an advantageous operation, however, depends to a considerable extent on the nature of the electroplating plating solution being utilized. It has been found for instance that conventional plating tank solutions deleteriously affected the efficiency and operability of the process which for its success depends on the utilization of high current densities, rapid electrodeposition rates and which is necessarily accompanied by severe agitation or turbulence of the electroplating solution due to the rapidly rotating honing tool. Further the anode or honing too] must not be polarized or corroded by the plating solution and the speed of deposition ranges between 3-30 microns/min, preferably between '12-30 microns/min. Additionally the adhesion of the deposit to the metal base and the physical properties of the resulting deposit must be equal or superior to those of the conventional platings. Furthermore, because of the insolubility of the anode honing tool the plating solution must be able to be used for a practical length of time without significant alteration of its deposition characteristics and it must be capable of being chemically replenished.

It has now been found that a significant improvement in a simultaneous electroplating, machining operation can be realized by delivering to the surface of the workpiece to'be electroplated in such an operation, while the machining tool is being rotated and while passing current from the anode (machining tool) to the cathode (conductive workpiece) at an elevated current density, an aqueous metal plating solution selected from the group consisting of:

a. a bronze electroplating solution comprising an aqueous alkaline solution of a water-soluble tin salt present in amounts to provide a tin concentration expressed as elemental tin of 40-170 g/l anda watersoluble copper salt to provide a copper concentration expressed as elemental copper of 30-70 g/l, said solution having a pH of 9-14 and being maintained during the operation at a temperature of 4090C., the current being delivered at a current density of from about -210 amperes per square dm whereby bronze is deposited on said surface of the workpiece being plated and machined at a rate of about 3-30 microns/min;

b. a cobalt electroplating solution comprising an aqueous solution of a water-soluble cobalt salt present in amounts to provide a cobalt concentration expressed as elemental cobalt of 20-250 g/l, said electroplating solution having a pH of 1-5.5 and being maintained during the plating and machining operation at a temperature of 2090C, the current being delivered at a current density of from about 50-300 amperesper square dm whereby cobalt is deposited on said surface to be plated at a rate of about 3 to 30 microns/min; and

c'. a chromium electroplating solution comprising an aqueous solutionof chromic acid present in amounts of about -600 g/l, said-solution having a pH of about 1.0 to 6.6 and being maintained during the operation at a temperature of about 1580C, said current being delivered at a current density of about 100-450 amperes per square drn whereby chromium is deposited on said surface of the workpiece being plated and machined at a rate of about 3-30 microns/min.

Advantageously, the above plating solutions can be recycled through the electroplating solution reservoir where the metal concentration can be replenished.

During the operation of electroplating and machining the workpiece, the honing tool is rotated thereby creating strong agitation or turbulence in the electroplating solution being delivered to the surface of the workpiece being electroplated. As indicated above, under these. conditions and with the use of high current densities to achieve rapid electrodeposition rates, convention a1 electroplating solutions have been found to be generally unsatisfactory.

in the following examples a metallic workpiece having a hole therein to be simultaneously electroplated and honed was inserted in a workpiece holder to maintain the same stationary during the operation. The rotatable honing tool is positioned in the apparatus with the surface of the hole of the workpiece spaced from the tool. The operator then causes the tool to rotate, delivers the electroplating solution to the surface of the hole in the workpiece to be electroplated and causes a DC. current to pass from the tool through the electroplating solution to the workpiece, thereby causing the metal in the electroplating solution to be deposited on said surface. As the electrodeposit builds upon this surface, the honing faces of the tool can be intermittently urged against the surface being electroplated and retracted therefrom, at predetermined rates so that the electroplate can build up uniformly at a high rate, and honed while it increases. The operation is discontinued when predetermined tolerances for the diameter are achieved. The deposits obtained with these solutions are harder, have compressive stresses which is a good property for bore surfaces with a good adhesion and less than harmful hydrogen content. The bronze and cobalt deposits show a banded structure different from the columnar one obtained in normal plating. Representative metal workpieces include cast iron, 4340 steel, stainless steel and aluminum alloys.

EXAMPLE 1 The internal diameter of a steel workpiece is simultaneously machined and electroplated in the process described above using the bronze .plating solution described below under the following conditions:

Plating Solution K SnO JH O 364 g/l CuCN 80 g/l KCN I45 g/l KOH g/l Temperature 70 Alloy Tin Content 7-127: Cathodic Current Density 200 amp/dm Speed of Rotating Honing Tool 150 r.p.m.

Speed of Deposition 20 microns/min EXAMPLE 2 The internal diameter of a steel workpiece is simultaneously machined and electroplated in the process described above using the cobalt plating solution described below under the following conditions:

Plating Solution Co(SO NH,)= 335 g/l H 80 20 g/l Temperature 60C Cathodic Current Density 200 amp/dm Speed of Rotating Honing Tool 150 r.p.m.

Speed of Deposition l2 microns/min EXAMPLE 3 The internal diameter of a steel workpiece is simultaneously machined and electroplated in the process described above using the chromium plating solution described below under the following conditions:

Plating Solution Preferred r0 300 g/l Nar CrO 100 g/l b13 50, 4 g/l Temperature 2 S C Cathodic Current Density 420 amp/dm Speed of Rotating Honing Tool 150 r.p.m,

Speed of Deposition 20 microns/min What is claimed is: t 1. In -a method of simultaneously electroplating a conductive workpiece by electrodepositing a metal on a surface of said workpiece to be plated and selectively machining said surface on which said metal is being electrodeposited by intermittently urging a rotating machining tool against said surface of said workpiece being plated, said workpiece serving as a cathode and said rotating machining tool serving as an anode, the improvement comprising delivering an aqueous metal plating solution to said surface to be plated while said machining tool is rotating and passing current from said anode to said cathode at an elevated current density to deposit said metal on said surface, said aqueous metal plating solution being selected from the group consisting of:

a. a bronze electroplating solution comprising an aqueous alkaline solution of a water-soluble tin salt present in amounts to provide a tin concentration expressed as elemental tin of 40-170 g/l and a water-soluble copper salt to provide a copper concentratin expressed as elemental copper of 30-70 g/l, said solution having a pH of 9-14 and being maintained at a temperature of 4090C, said current being delivered at a current density of from about -210 amperes per square dm whereby bronze is deposited on said surface to be plated at a rate of about 3-30 microns/min;

b. a cobalt electroplating solution comprising an aqueous solution of a water-soluble cobalt salt present in amounts to provide a cobalt concentration expressed as elemental cobalt of 20-250 g/l, said solution having a pH of 1-5.5 and being maintained at a temperature of 2090C, said current being delivered at a current density of from about 50-300 amperesper square dm whereby cobalt is deposited on said surface to be plated at a rate of about 3 to 30 microns/min; and

c. a chromium electroplating solution comprising an aqueous solution of chromium acid present in amounts of about -600 g/l, said solution having a pH of about 1.0 to 6.6 and being maintained at a temperature of about l5-80C, said current being delivered at a current density of from about 100-450 amperes per square dm whereby chromium is deposited on said surface to be plated at a rate of about 3-30 microns/min.

2. The method of claim 1 which includes recovering spent electroplating solution, adjusting the plating metal content thereof to a preplating concentration range and recycling said solution to the electroplating operation. 

2. The method of claim 1 which includes recovering spent electroplating solution, adjusting the plating metal content thereof to a preplating concentration range and recycling said solution to the electroplating operation. 